Completely intracorporeal pulsatile blood pump systems require some means of compensation for the volume changes which occur within the blood pump with each stroke of the pump. This remains a significant problem in the development of totally implantable artificial heart systems and to date, a good system has not been developed. Preliminary studies have been conducted with intrathoracic compliance chambers implanted in calves. The most recent results with textured surface chambers have been very promising with respect to function and tissue encapsulation, although the number of experiments (3) is very limited at this time. These studies did not, however, provide data relative to gas transfer across the elastomeric membrane--a significant problem for long-term stability. The specific objectives of the proposed program are: 1) to demonstrate the reproducibility of the results with respect to the biological and functional compatibiliity of Dacron velour surface intrathoracic compliance chambers for totally implantable cardiac prostheses for two years, 2) evaluate Hexysn (polyolefin rubber), which has an inherent low gas permeability and extremely long flex life, as the chamber diaphragm and 3) to study the long-term effects of gas and water vapor transfer across the compliance membrane, both in vitro and in vivo. Hexsyn rubber permeability characterization will be done in vitro prior to in vivo experimentation. Six 6-month and two 24-month in vivo experiments will be performed. An implantable metal bellows actuation unit will confine gas and water vapor transmission to the membrane only. The chambers will be filled with a preconditioned gas mixture at predicted in vivo equilibrium gas and water vapor partial pressures. Further studies, as described in this proposal, are required to demonstrate the reproducibility and practial application of this solution to the variable volume problem of totally implantable cardiac prostheses and address other factors such as membrane durability and permeability, and the compliance fluid characteristics and interfacing requirements relative to the various implantable blood pump systems under development.